1. Field of the Invention
The present invention relates generally to electronic devices such as light emitting diodes (LEDs), and more particularly to a method of making an electronic device having a single crystal substrate formed from a polycrystalline material.
2. Description of the Related Art
LEDs, laser diodes, and other electronic devices are typically manufactured by depositing various layers of semiconductor materials on a substrate. A know group of semiconductor materials which is useful in forming light-emitting devices is the gallium nitride (GaN) system. The gallium nitride system refers to semiconductor materials comprising one or more of the group III nitrides, GaN, AIN, and InN. The GaN system allows various wavelengths of light, particularly the shorter wavelengths, to be produced based on the relative amounts of GaN, AIN, and InN in the composition.
Gallium nitride-based semiconductor devices are commonly formed on a substrate comprising sapphire, a single crystal alumina (Al.sub.2 O.sub.3). Typically, the sapphire substrate is produced by growing a single alumina crystal from molten alumina, and subsequently cutting the sapphire body in the shape of a thin wafer. However, the process of growing a sapphire crystal from a melt is relatively expensive due to the need to carefully control the growing conditions. In addition, the resulting crystal typically must be cut with a diamond saw, ground, and polished into the shape of a wafer. In addition to being expensive, this process limits the types of shapes which can be produced.
It would be desirable, therefore, to have a process for forming a sapphire substrate which decreased the amount of cutting, grinding and polishing required, thereby decreasing the cost of the substrate, and which could be used to form substrates of a variety of shapes useful for different electronic devices.